The term “poly-plane imaging unit” shall hereinafter be taken to mean an imaging unit comprising not just one pivotal plane, but a plurality of pivotal planes, in particular two or three, for image recording.
This invention relates in particular to angiography systems as are used for interventional procedures, for example on the heart. Traditionally angiography systems produce simple X-ray projection images on which structures such as heart shadows, guide wires, catheters and contrast-medium filled catheters can be seen. Typically newer-design angiography devices comprise a C-shaped arm, on one end of which an X-ray source is attached and on the other end of which an associated X-ray detector is attached. The C-arm can pivot freely about a patient couch and thereby allows two-dimensional real time X-ray images (fluoroscopy images) of the patient to be recorded from a wide variety of viewing directions. Such angiography systems can therefore also produce CT-like 3D images by rotating the C-arm around the patient, and this is also called a C-arm CT.
To use computed tomography and other three-dimensional reconstruction methods, such as PET (Positron Emission Tomography), SPECT (Single Photon Emission Computed Tomography) or MR (Magnetic Resonance) it is necessary for the data required for the respective modality of the image capture, from which a volume data element is to be produced, to match a precisely defined state of the examination object. In reality this is not always the case however as with many examination objects breathing, heartbeat or peristalsis, for example, cause movements in the examination object. Such movements cause artifacts in the images produced which sometimes significantly restrict or even entirely prevent clinical use of these representations. This problem occurs particularly clearly in the case of continually moving examination objects, such as the heart for example.
While an attempt can be made to remedy this problem by reducing the recording time of the raw data by way of quicker rotational movements of the CT device or by using two CT devices, this approach is not suitable for current C-arm devices.
A reverse method for solving this problem lies in selecting input data which matches a precisely defined state of the examination object and, more precisely, subsequently by what is known as “gating” (for example only using input data corresponding to a cardiac phase measured by means of an ECG or by using breathing sensors) or during data acquisition by “triggering”, i.e. data are only recorded if a signal, for example from an ECG or a breathing sensor, indicates that the examination object is in the desired state). However this requires long times for data acquisition, and this leads to problems in particular if contrast medium is used or if for example further movements have to be suppressed by holding one's breath. The use of this approach also assumes that the movement of the examination object is periodic, and this is not the case for example with a movement caused by a combination of breathing and heartbeat or by arrhythmias.